1. Field of the Invention
The invention, in general, relates to a novel outside air thermometer and, more particularly, to an outside air thermometer provided, in a common housing having air intake and output openings, with a temperature sensor and a device including an electrically powered blower for forced ventilation.
2. The Prior Art
Such outside air thermometers are used as stationary apparatus in weather stations. They serve to measure the air temperature prevailing at the measuring site as precisely as possible and undistorted by sun irradiation or vaporization effects. For this purpose, the actual sensors of such apparatus are insulated by being mounted in double-walled housings which are open at their top and bottom and are provided with an active forced ventilation system. For measuring the temperature, an electrically driven blower sucks ambient air through the chamber formed by the inner wall of the double-walled housing provided with the sensor and, at the same time, for cooling the housing heated by sun irradiation it sucks ambient temperature through the outer chamber formed for insulation between the inner and outer wall of the double-walled housing. The forced feeding of air in the sequence of intake opening-sensor-blower-output opening prevents the heat loss or dissipation of the blower from reverting to the sensor and distorting the result of the measurement.
In principle such a system operates satisfactorily, even with strong blowers, in respect of many common ambient conditions, particularly in regions subject to strong sun radiation. However, in areas where strong winds prevail, such as, for instance, coastal regions, mountains or in antarctica, the result of measurements may be distorted by the fact that wind blowing at speeds exceeding 15 m/sec may lead to air-flow reversal in the interior of the temperature gage, increased forced air feeding notwithstanding. Depending upon the angle at which the wind impinges the dynamic head may cancel the counter pressure of the blower and affect an reverse flow of air which feeds the heat dissipated by the blower to the temperature sensor. For reasons of energy efficiency, the power of the blower cannot be arbitrarily be raised, especially in uninhabited regions, because the required energy either is not available or because of the increasing heat loss of an enlarged blower and the housing in which it is mounted which would have to be disproportionately large.
For specific purposes, numerous systems are available in the area of external air temperature measuring. In particular, in automotive technology measuring the air temperature surrounding internal combustion engines is used for managing engines in a manner satisfying all environmental conditions as they develop. Fuel mixtures, ignition timing, etc. are optimized by way of the ambient air temperature as well as engine or coolant temperature not only for satisfactory cold starting conditions but also for operation after the engine has warmed up. Such uses do not require precision measurement of the kind necessary for scientific research. Also, in moving measuring systems the impact of heat loss sources may be reduced by making use of the moving air. However, in stationary measuring systems of the kind used in meteorology for weather forecasts and other research systems, protection from sun irradiation and other weather conditions such as wind, dew, etc. is of decisive importance.
From German DE 43 34 509 a thermometer for measuring outside temperature is known which can be mounted on the wall of houses. For protecting it from sun irradiation, its temperature sensor is mounted in a tube through which an external air current is flowing from below in an upward direction. It is forced by an electrically powered blower disposed above the temperature sensor. Behind the blower, the air is dispersed upwardly between the housing of the measuring system and the wall of the house such that the air heated by the blower cannot reach the sensor. The entire system is provided with electric current for the blower and the measuring electronics by a solar panel integrated into the front wall of the housing of the apparatus. The mounting on the wall of a house is disadvantageous which, by being heated by sun irradiation, generates an upwardly directed thermic and which feeds air to the measuring apparatus which is too warm and distorted with respect to the temperature of the ambient air. This circumstance and the provision of the system with solar cells and radiation protection tube which make mounting the apparatus at a location exposed to sun irradiation mandatory, contradict each other so that at least as to more stringent measurement requirements satisfactory results may are not to be expected. Moreover, turbulence occurring at the wall of a house at strong winds may lead to wrong results if the air because of a dynamic head above the measuring apparatus is caused to flow through the air channel downwardly from above so that the heat dispersion of the blower distorts the measuring result at the sensor.
Professional outside air thermometers provided as standard equipment with stepped radiation protection (Type 430) or, optionally, (Type 440) with forced air feeding by means of blowers, are respectively known from Internet product specifications “Temperatursensor Mit Strahlungsschutz und Zwangsbelueftung, Wetterhuette Type 430” (www.koneis.at/download/430_dT.pdf) and “Wetterhuette Type 440” (www.kroneis.at/download/440.pdf). Both apparatus are intended for exposed mounting on masts in weather stations. Protection from measuring value distortions in case of strong wind is not provided for either apparatus. Another Internet product specification “Temperatur, Elektrische Messwertgeber” (www.thiesclima.com/temperatur/elektrische_messwertgeber.htm#lufttemp), which being the closest state of prior art forms the basis of the instant invention, also discloses a professional outside air thermometer (ventilated air temperature gage) which in addition to the common radiation protection is provided with forced air ventilation by means of blowers as standard equipment. This apparatus, too, is intended for exposed mounting, yet no provision is made for protection from distorted measurement values as a result of strong wind.
The state of the art seems to indicate that the distorting effect of strong wind is either not known to either manufacturers or users or is considered to be negligible.